The letter was signed by 19 staff members.
The board says it is conducting an internal review. The Corporation for Public Broadcasting will also be conducting an external review.
An anonymous complaint was lodged against the television station in December, prompting the federal CPB to launch an inquiry.
The station is not allowed to spend any of the approximately $1 million it receives annually - about 16 percent of its operating budget - until the matter is resolved, according to reports.